How to validate if Task has a picture attached

Summary: We allow Techs to Complete / Suspend an Activity based on few checks.

One of those checks is - to ensure a picture or file has been attached.

Content (please ensure you mask any confidential information):

While setting up visibility conditions - we dont see fields that have the type set as 'file'. If I wanted to validate - that the user has attached at least one File or Attachment, how can this be achieved.

For example : I am using the following as a validation and it seems this is not supported either:

Define a property to indicate if the file has been attached.